JP7790239B2 - Electrostatic image developing carrier, electrostatic image developer, process cartridge, image forming apparatus and image forming method - Google Patents

Description

The present invention relates to a carrier for developing electrostatic images, an electrostatic image developer, a process cartridge, an image forming apparatus, and an image forming method.

Patent Document 1 discloses a carrier for developing electrostatic images, which has a core material and a coating resin layer that contains nitrogen-containing resin particles and inorganic oxide particles and coats the core material, and the surface exposure rate of the nitrogen-containing resin particles is 0.8% or more and 3.0% or less.
Patent Document 2 discloses an electrostatic latent image developing carrier in which the surface of core particles is coated with a matrix resin, and in which two or more types of nitrogen-containing fine particles are contained in the matrix resin, and among the fine particles, relatively large fine particles have a primary average particle diameter in the range of 0.1 to 3.0 μm, and relatively small fine particles have a primary average particle diameter in the range of 0.01 to 0.1 μm, and the ratio of the primary average particle diameters of the two is in the range of 300:1 to 2:1.

Japanese Patent Application Laid-Open No. 2021-51216 Japanese Patent Application Laid-Open No. 2001-51454

When a large amount of fine particles is added to the resin coating layer of the carrier, the strength of the coating layer is improved due to the filler effect, and carrier contamination by external additives attached to the toner can be suppressed, resulting in an improvement in the charge retention of the carrier. However, when high stress is applied to the carrier, such as when the image density is low, such as when the ratio of the image to the paper surface is 1%, when short printing of about 100 sheets in a single job is performed, or when long-term printing of 50,000 sheets or more is performed continuously, the resin coating layer may peel off even in a resin coating layer containing fine particles, and the charge retention may deteriorate.
The present invention aims to suppress deterioration of the charge retention of a carrier in a resin coating layer containing nitrogen-containing silica particles and nitrogen-containing resin microparticles, compared to when the nitrogen-containing silica particle content is less than 10 mass % or more than 55 mass % relative to the total mass of the resin coating layer.

The invention of claim 1 is a carrier for developing electrostatic images, comprising a core material and a resin coating layer containing nitrogen-containing silica particles and nitrogen-containing resin microparticles and coating the core material, wherein the content of the nitrogen-containing silica particles is 10 mass% or more and 55 mass% or less relative to the total mass of the resin coating layer, the volume-average particle diameter of the nitrogen-containing resin microparticles is 100 nm or more and 250 nm or less, and the mass ratio P/S of the mass P of the nitrogen-containing resin microparticles to the mass S of the nitrogen-containing silica particles is 0.15 or more and 0.55 or less.
The invention of claim 2 is the carrier for developing electrostatic images according to claim 1, wherein the nitrogen-containing silica particles include silica particles treated with a silane coupling agent having a nitrogen-containing functional group, or a vinyl copolymer synthesized from a (meth)acrylic monomer having a nitrogen-containing functional group and a hydrolyzable alkoxysilanol group.
A third aspect of the present invention is the electrostatic image developing carrier according to the second aspect, wherein the silane coupling agent having a nitrogen-containing functional group has an amino group and a hydrolyzable alkoxysilanol group.
A fourth aspect of the present invention is the electrostatic image developing carrier according to the third aspect, wherein the nitrogen-containing silica particles have a volume average particle size of 5 nm or more and 20 nm or less.
The invention of claim 5 is the carrier for developing electrostatic images according to claim 1, wherein, when the volume average particle diameter of the nitrogen-containing resin microparticles is D (μm) and the thickness of the resin coating layer is T (μm), D/T is 0.007 or more and 0.24 or less.
A sixth aspect of the present invention is the electrostatic image developing carrier according to the fifth aspect, wherein the content of the nitrogen-containing resin fine particles is 5% by mass or more and 30% by mass or less with respect to the total mass of the resin coating layer.
A seventh aspect of the present invention is the carrier for developing electrostatic images according to the fifth aspect, wherein the nitrogen-containing resin fine particles have a volume average particle size of 120 nm or more and 230 nm or less.
An eighth aspect of the present invention is the electrostatic image developing carrier according to the first aspect, wherein the resin coating layer contains an alicyclic (meth)acrylic resin.
A ninth aspect of the present invention is the electrostatic image developing carrier according to the eighth aspect, wherein the alicyclic (meth)acrylic resin contains cyclohexyl (meth)acrylate as a polymerization component.
A tenth aspect of the present invention is the electrostatic image developing carrier according to the first aspect, wherein the content of the nitrogen-containing silica particles is 13% by mass or more and 50% by mass or less with respect to the total mass of the resin coating layer.
The invention of claim 11 is the carrier for developing electrostatic images according to claim 10, wherein the mass ratio P/S of the mass S of the nitrogen-containing silica particles to the mass P of the nitrogen-containing resin fine particles is 0.18 or more and 0.52 or less.
The invention of claim 12 is an electrostatic image developer containing a toner for developing electrostatic images and the carrier for developing electrostatic images according to any one of claims 1 to 11.
The invention of claim 13 is a process cartridge that is detachably attached to an image forming apparatus and contains the electrostatic image developer described in claim 12 and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.
The invention of claim 14 is an image forming apparatus comprising an image carrier, charging means for charging the surface of the image carrier, electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier, developing means that contains the electrostatic image developer of claim 12 and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, transfer means that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and fixing means that fixes the toner image transferred to the surface of the recording medium.
The invention of claim 15 is an image forming method comprising: a charging step of charging the surface of an image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer of claim 12; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; and a fixing step of fixing the toner image transferred to the surface of the recording medium.

According to the invention of claim 1, in a carrier for developing electrostatic images containing nitrogen-containing silica particles and nitrogen-containing resin microparticles in a resin coating layer, deterioration of the carrier's charge retention can be suppressed compared to when the nitrogen-containing silica particle content is less than 10 mass% or more than 55 mass% relative to the total mass of the resin coating layer, or when the volume average particle size of the nitrogen-containing resin microparticles is less than 100 nm or more than 250 nm.
According to the invention of claim 2, it is possible to provide a carrier for developing electrostatic images in which the charge distribution in the nitrogen-containing silica is narrower than in a case in which the nitrogen-containing silica particles do not contain silica particles treated with a silane coupling agent having a nitrogen-containing functional group or a vinyl copolymer synthesized from a (meth)acrylic monomer having a nitrogen-containing functional group and a hydrolyzable alkoxysilanol group.
According to the invention of claim 3, it is possible to provide a carrier for developing electrostatic images in which the charge distribution in the nitrogen-containing silica is narrower than when the silane coupling agent does not have an amino group and a hydrolyzable alkoxysilanol group.
According to the invention of claim 4, it is possible to provide a carrier for developing electrostatic images in which the charge distribution of the nitrogen-containing silica is narrower than when the volume average particle diameter of the nitrogen-containing silica particles is less than 5 nm or more than 20 nm.
According to the invention of claim 5, when the volume average particle diameter of the nitrogen-containing resin microparticles is D (μm) and the thickness of the resin coating layer is T (μm), it is possible to provide a carrier for developing electrostatic images in which deterioration of charge retention is suppressed compared to when D/T is less than 0.007 or greater than 0.24.
According to the invention of claim 6, it is possible to provide a carrier for developing electrostatic images in which deterioration of charge retention is suppressed compared to when the content of the nitrogen-containing resin microparticles is less than 5 mass % or more than 30 mass % relative to the total mass of the resin coating layer.
According to the seventh aspect of the present invention, it is possible to provide a carrier for developing electrostatic images in which deterioration of charge retention is suppressed compared to when the volume average particle diameter of the nitrogen-containing resin microparticles is less than 120 nm or more than 230 nm.
According to the eighth aspect of the present invention, it is possible to provide a carrier for developing electrostatic images in which the particle dispersibility in the resin coating layer is improved compared to when the resin coating layer does not contain an alicyclic (meth)acrylic resin.
According to the ninth aspect of the present invention, it is possible to provide a carrier for developing electrostatic images in which the influence of moisture due to environmental changes is suppressed, compared to when the alicyclic (meth)acrylic resin does not contain cyclohexyl (meth)acrylate as a polymerization component.
According to the invention of claim 10, it is possible to provide a carrier for developing electrostatic images in which deterioration of charge retention is suppressed compared to when the content of the nitrogen-containing silica particles is less than 13 mass % or more than 50 mass % relative to the total mass of the resin coating layer.
According to the invention of claim 11, a carrier for developing electrostatic images can be provided in which deterioration of charge retention is suppressed compared to when the mass ratio P/S of the nitrogen-containing resin microparticles to the mass S of the nitrogen-containing silica particles is less than 0.18 or greater than 0.52.
According to the invention of claim 12, 13, 14 or 15, in a carrier for developing electrostatic images containing nitrogen-containing silica particles and nitrogen-containing resin microparticles in a resin coating layer, it is possible to provide an electrostatic image developer, a process cartridge, an image forming apparatus or an image forming method in which deterioration of charge retention is suppressed compared to when the nitrogen-containing silica particle content is less than 10 mass % or more than 55 mass % relative to the total mass of the resin coating layer, or when the nitrogen-containing resin microparticles have a volume average particle size of less than 100 nm or more than 250 nm.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention.

The following describes embodiments of the invention. These descriptions and examples are intended to illustrate embodiments and do not limit the scope of the invention.

In this disclosure, the expressions "from XX to XX" or "XX to XX" that represent a numerical range mean a numerical range including the stated upper and lower limits, unless otherwise specified. Furthermore, in this disclosure, when referring to the amount of each component in a composition, if the composition contains multiple substances corresponding to each component, the expression means the total amount of those multiple substances present in the composition, unless otherwise specified.
In the present disclosure, the "electrostatic image developing carrier" may be simply referred to as the "carrier," the "electrostatic image developing toner" may be simply referred to as the "toner," and the "electrostatic image developer" may be simply referred to as the "developer."

<Electrostatic image developing carrier>
The carrier for developing electrostatic images according to this embodiment has a core material and a resin coating layer that contains nitrogen-containing silica particles and nitrogen-containing resin fine particles and coats the core material, wherein the content of the nitrogen-containing silica particles is 10% by mass or more and 55% by mass or less relative to the total mass of the resin coating layer, the volume-average particle diameter of the nitrogen-containing resin fine particles is 100 nm or more and 250 nm or less, and the mass ratio P/S of the mass P of the nitrogen-containing resin fine particles to the mass S of the nitrogen-containing silica particles is 0.15 or more and 0.55 or less.

When the resin coating layer that coats the core material of the carrier for developing electrostatic images contains a large amount of fine particles such as inorganic oxide particles and resin fine particles, the filler effect improves the strength of the resin coating layer and makes it easier for unevenness to occur on the carrier surface, thereby suppressing carrier contamination by external additives adhering to the toner, and as a result, has the effect of improving the charge retention of the carrier.
However, under conditions where high stress is applied to the carrier, such as when the image density is low (e.g., 1% of the paper), when short print runs of about 100 sheets are repeated in one job, or when long-term runs of 50,000 sheets or more are performed, peeling of the resin coating layer occurs even when the carrier contains fine particles. As this peeling progresses, the charge retention of the entire developer may deteriorate.
The carrier according to the present embodiment has the above-described structure, and therefore can suppress deterioration of the charge retention even in an environment where high stress is applied and the resin coating layer of the carrier is likely to peel off. The mechanism behind this is presumed to be as follows.
In this embodiment, nitrogen-containing silica particles and nitrogen-containing resin microparticles are contained in the resin coating layer. Mutual repulsion of the nitrogen elements occurs between the nitrogen-containing silica particles and the nitrogen-containing resin microparticles, improving the dispersion of each particle, suppressing uneven distribution of each particle within the resin coating layer, and enhancing the filler effect. As a result, even under high-stress conditions (such as low image density) where the resin coating layer is prone to peeling, the nitrogen-containing silica particles are always uniformly present on the surface of the resin coating layer, providing a carrier with excellent charge retention.
Although titanate compound particles may also be used as inorganic particles in carriers, in this embodiment, silica particles, not titanate compound particles, are used as nitrogen-containing inorganic particles, and are effective in improving charge retention. The reason for this is presumed to be as follows: Titanium has a stronger positive charge than silica, so in nitrogen-containing titanate particles, when the positive charge of the nitrogen element is added to the positive charge of titanium, the repulsion between the nitrogen elements described above becomes excessive, worsening the dispersibility of the particles, and titanium, which has good charge exchange properties, is unevenly distributed on the surface of the resin coating layer, thereby worsening the charge retention.

The configuration of the carrier according to this embodiment will be described in detail below.
[Core material]
The electrostatic image developing carrier according to this embodiment contains a core material.
The core material is not particularly limited as long as it has magnetic properties, and any known material used as a core material for a carrier can be used.
Examples of the core material include particulate magnetic powder (magnetic particles), resin-impregnated magnetic particles in which porous magnetic powder is impregnated with resin, and magnetic powder-dispersed resin particles in which magnetic powder is dispersed in resin. One type of core material may be used alone, or two or more types may be used in combination.

Examples of magnetic particles include particles of magnetic metals such as iron, nickel, and cobalt; and magnetic oxides such as ferrite and magnetite, with magnetic oxide particles being preferred.
Examples of resins that may be used for the core include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic acid ester copolymer, straight silicone or modified silicone containing organosiloxane bonds, fluororesin, polyester, polycarbonate, phenolic resin, and epoxy resin. These resins may be used alone or in combination of two or more. The resin that may be used for the core may contain additives such as conductive particles. Examples of conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

The core material is preferably a particulate magnetic powder, that is, magnetic particles.
The volume average particle size of the magnetic particles is preferably, for example, 20 μm or more and 50 μm or less.

[Resin coating layer]
The resin coating layer according to this embodiment contains nitrogen-containing silica particles and nitrogen-containing resin fine particles.
The resin coating layer according to this embodiment is a resin layer that coats the core material.

(Binder resin)
Examples of binder resins constituting the resin coating layer include styrene-acrylic acid copolymers, polyolefin resins such as polyethylene and polypropylene, polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone, vinyl chloride-vinyl acetate copolymers, straight silicone resins or modified products thereof consisting of organosiloxane bonds, fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride and polychlorotrifluoroethylene, polyesters, polyurethanes, polycarbonates, amino resins such as urea-formaldehyde resins, and epoxy resins. The resins constituting the resin coating layer may be used alone or in combination of two or more.

The resin that makes up the resin coating layer preferably contains an alicyclic (meth)acrylic resin. When the resin coating layer contains an alicyclic acrylic resin, the inorganic oxide particles contained in the resin coating layer tend to be more dispersible, and resin fragments containing inorganic oxide particles tend to be generated more efficiently. As a result, density unevenness in the image tends to be further suppressed.

As the polymerization component of the alicyclic (meth)acrylic resin, a lower alkyl ester of (meth)acrylic acid (for example, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 9 carbon atoms) is preferred, and specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and 2-(dimethylamino)ethyl (meth)acrylate.
Among the above, from the viewpoint of further suppressing uneven density of an image, the polymerizable component of the alicyclic acrylic resin preferably contains at least one selected from the group consisting of methyl(meth)acrylate, cyclohexyl(meth)acrylate, and 2-(dimethylamino)ethyl(meth)acrylate, and more preferably contains at least one of methyl(meth)acrylate and cyclohexyl(meth)acrylate. The polymerizable component of the alicyclic acrylic resin may be used alone or in combination of two or more.

Alicyclic (meth)acrylic resins shield the influence of water on the polarized component of the carbon-oxygen bond due to the steric hindrance of the alicyclic functional group. It is preferable to include cyclohexyl (meth)acrylate as a polymerization component because this can suppress the influence of moisture in environmental changes.
The content of cyclohexyl (meth)acrylate contained in the alicyclic (meth)acrylic resin is preferably 75 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and even more preferably 95 mol% or more and 100 mol% or less.

Methods for forming a resin coating layer on the surface of a core material include, for example, wet and dry processes. A wet process uses a solvent to dissolve or disperse the resin that makes up the resin coating layer. A dry process, on the other hand, does not use such a solvent.

Examples of wet manufacturing methods include a dipping method in which a core material is dipped in a resin liquid for forming a resin coating layer to coat it; a spraying method in which a resin liquid for forming a resin coating layer is sprayed onto the surface of a core material; a fluidized bed method in which a core material is fluidized in a fluidized bed and a resin liquid for forming a resin coating layer is sprayed onto the core material; and a kneader coater method in which a core material and a resin liquid for forming a resin coating layer are mixed in a kneader coater and the solvent is removed.
The resin liquid for forming the resin coating layer used in the wet manufacturing method is prepared by dissolving or dispersing the resin and other components in a solvent. The solvent is not particularly limited as long as it can dissolve or disperse the resin, and examples of the solvent that can be used include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane.
An example of a dry manufacturing method is a method in which a mixture of a core material and a resin for forming a resin coating layer is heated in a dry state to form a resin coating layer. Specifically, for example, the core material and the resin for forming the resin coating layer are mixed in a gas phase and heated to melt, thereby forming a resin coating layer.

The thickness of the resin coating layer is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 5 μm or less, and even more preferably 0.3 μm or more and 3 μm or less.
The thickness of the resin coating layer is measured by the following method. The carrier is embedded in an epoxy resin or the like, and then cut with a diamond knife or the like to prepare a thin section. This thin section is observed with a transmission electron microscope (TEM) or the like, and cross-sectional images of multiple carrier particles are taken. The thickness of the coating layer is measured at 20 points from the cross-sectional images of the carrier particles, and the average value is used.

(Nitrogen-containing silica particles)
The nitrogen-containing silica particles contained in the resin coating layer contain nitrogen elements by reacting or adhering a nitrogen-containing substance to the silica particles, etc. It is preferable to subject the silica particles to a surface treatment with the nitrogen-containing substance.
The nitrogen-containing substance used for the surface treatment of the core particles is preferably a silane coupling agent having a nitrogen-containing functional group or a vinyl copolymer synthesized from a (meth)acrylic monomer having a nitrogen-containing functional group and a hydrolyzable alkoxysilanol group.The hydroxyl groups present on the surface of silica particles are highly active, smoothly promoting the hydrolysis of the silanol groups of the silane coupling agent and the silanol groups of the vinyl copolymer, so that no unreacted surface treatment agent remains on the surface of the silica particles.Therefore, a carrier formed by dispersing nitrogen-containing silica particles treated with the surface treatment agent in a matrix resin to form a resin coating layer does not contain unreacted silane coupling agent originating from silica particles, and there is no problem that the silane coupling agent migrates to the carrier surface over time, changing the carrier's charge retention.

Examples of the nitrogen-containing functional group include an amino group, an amide group, an imide group, and an amide-imide group. In particular, an amino group is preferred in terms of narrowing the charge distribution in silica particles and improving the charge retention of the carrier. In addition, examples of the hydrolyzable alkoxysilanol group reactive with a hydroxyl group include a trimethoxysilyl group, a triethoxysilyl group, a dimethoxysilyl group, and a diethoxysilyl group. Therefore, a silane coupling agent having an amino group and a hydrolyzable alkoxysilanol group is preferred.
Specific examples of the silane coupling agent having a nitrogen-containing functional group used in this embodiment are as follows:
_H2N ( _CH2 ) _3Si ( _OCH3 ) _{3
H2N ( CH2} ) _3Si ( _OC2H5 ) _3
H2N ( _CH2 ) ₃ ( _CH3 ) _2Si ( _{OC2H5 )
H2N ( CH2} ) ₃ ( _CH3 )Si( _OC2H5 ) _2
H2N ( _CH2 ) _2NH ( _CH2 )Si( _OCH3 ) _3
H2N ( _CH2 ) _2NH ( _CH2 ) _3Si ( _OCH3 ) _3
H2N ( _CH2 ) _2NH ( _CH2 ) ₂ ( _CH3 )Si( _OCH3 ) _2
H2NCONH ( _CH2 ) _3Si (OCH3) _{3
H2NCONH ( CH2} ) _3Si ( _OC2H5 ) _3
H2N ( _CH2 ) _2NH ( _CH2 ) _2NH ( _CH2 ) _3Si ( _OCH3 ) ₃
( _CH3 ) _2N ( _CH2 ) ₂ ( _CH3 )Si( _{OC2H5 ) 2}
( _{C4H9 ) 2N} ( _CH2 ) _3Si ( _OCH3 ) _3
C3H7 ( _CH3 ) _N ( _CH2 ) _3Si ( _OCH3 ) ₃

From the viewpoint of improving the charge retention of the carrier, the content of the nitrogen-containing silica particles in this embodiment is set to 10% by mass or more and 55% by mass or less, based on the total mass of the resin coating layer. It is more preferable that it is 13% by mass or more and 50% by mass or less, and even more preferable that it is 15% by mass or more and 45% by mass or less.

From the viewpoint of improving the charge retention of the carrier, the volume average particle size of the nitrogen-containing silica particles according to this embodiment is preferably 5 nm or more and 20 nm or less, more preferably 7 nm or more and 17 nm or less, and even more preferably 8 nm or more and 15 nm or less.
The volume average particle size of the nitrogen-containing silica particles is measured by observing a cross section of the carrier cut along the thickness direction with a scanning electron microscope and performing image analysis of the silica particles. Specifically, 50 nitrogen-containing silica particles per carrier are observed with a scanning electron microscope, and the longest and shortest diameters of each particle are measured by image analysis of the nitrogen-containing silica particles, and the equivalent sphere diameter is measured from the intermediate value. This measurement of the equivalent sphere diameter is performed for 100 carriers. The 50% diameter (D50v) of the volume-based cumulative frequency of the obtained equivalent sphere diameters is then taken as the volume average particle size of the silica particles.

In some cases, titanate compound particles are also used as inorganic particles in the carrier, but in this embodiment, silica particles are used as the nitrogen-containing inorganic particles because titanate compound particles deteriorate charge retention. The reason for this is presumed to be as follows: titanium has a stronger positive charge than silica, so in nitrogen-containing titanate particles, when the positive charge of titanium is added to the positive charge of nitrogen, the repulsion between the nitrogen elements described above becomes excessive, worsening particle dispersibility. It is also presumed that titanium, which has good charge exchange properties, is unevenly distributed on the surface of the resin coating layer, thereby worsening charge retention.

(Nitrogen-containing resin particles)
Examples of nitrogen-containing resin particles include particles of (meth)acrylic resins obtained by polymerizing dimethylaminoethyl (meth)acrylate, dimethylacrylamide, acrylonitrile, etc.; amino resins such as urea, melamine, guanamine, and aniline; amide resins; urethane resins; and copolymers of the above resins. Among these, from the viewpoint of further suppressing uneven density of images, the nitrogen-containing resin particles preferably contain particles of at least one type selected from the group consisting of amino resins and urethane resins, more preferably amino resin particles, and even more preferably melamine resin particles. The nitrogen-containing resin particles may be used alone or in combination of two or more types.

From the viewpoint of improving the charge retention of the carrier, the volume average particle diameter of the nitrogen-containing resin particles according to this embodiment is 100 nm or more and 250 nm or less. It is preferably 120 nm or more and 230 nm or less, and more preferably 140 nm or more and 220 nm or less. In particular, when the nitrogen-containing resin particles have a volume average particle diameter of 100 nm or more, they tend to easily form irregularities on the carrier surface, which tends to physically prevent external additives of the toner from adhering to the carrier.
The volume average particle size of the nitrogen-containing resin particles can be determined by the same method as that for the volume average particle size of the nitrogen-containing silica particles.

When the volume average particle size of the nitrogen-containing resin microparticles according to this embodiment is D (μm) and the thickness of the resin coating layer is T (μm), from the viewpoint of improving the charge retention of the carrier, D/T is preferably 0.007 or more and 0.24 or less. It is preferably 0.01 or more and 0.24 or less, more preferably 0.02 or more and 0.24 or less, and even more preferably 0.033 or more and 0.24 or less.

From the viewpoint of improving the charge retention of the carrier, the content of the nitrogen-containing resin particles in this embodiment is preferably 5% by mass or more and 30% by mass or less, more preferably 6% by mass or more and 20% by mass or less, and even more preferably 7% by mass or more and 15% by mass or less, relative to the total mass of the resin coating layer.

In this embodiment, the mass ratio P/S of the nitrogen-containing resin microparticles to the nitrogen-containing silica particles (S) is 0.15 or more and 0.55 or less, from the viewpoint of improving the carrier's charge retention. The mass ratio P/S is preferably 0.18 or more and 0.52 or less, and more preferably 0.20 or more and 0.50 or less.

<Electrostatic Image Developer>
The developer according to this embodiment contains the toner and the carrier according to this embodiment.

The developer according to this embodiment is prepared by mixing the toner and the carrier according to this embodiment in an appropriate ratio. The mixing ratio (mass ratio) of toner to carrier is preferably toner:carrier = 1:100 to 30:100, and more preferably 3:100 to 20:100.

[Toner for developing electrostatic images]
The toner is not particularly limited, and known toners can be used. For example, a colored toner containing toner particles containing a binder resin and a colorant can be used, and an infrared absorbing toner using an infrared absorbing agent instead of a colorant can also be used. The toner may contain a release agent, various internal additives, external additives, etc.

- Binder resin -
Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers.
Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these.
These binder resins may be used alone or in combination of two or more.

The binder resin is preferably a polyester resin, and examples of the polyester resin include known polyester resins.
The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower.
The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, it is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

The weight average molecular weight (Mw) of the polyester resin is preferably 5,000 to 1,000,000, more preferably 7,000 to 500,000. The number average molecular weight (Mn) of the polyester resin is preferably 2,000 to 100,000. The molecular weight distribution (Mw/Mn) of the polyester resin is preferably 1.5 to 100, more preferably 2 to 60.
The weight average molecular weight and number average molecular weight of the polyester resin are measured by gel permeation chromatography (GPC). Molecular weight measurement by GPC is performed using a Tosoh GPC HLC-8120GPC measuring instrument, a Tosoh TSKgel Super HM-M (15 cm) column, and a THF solvent. The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.
The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

- Coloring agent -
Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, Examples of suitable dyes include pigments such as ultramarine blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; and dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes.
The colorant may be used alone or in combination of two or more kinds.

The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.
The content of the colorant is preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

- Release agent -
Examples of the release agent include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral/petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters. However, the release agent is not limited to these.

The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower.
The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" as described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."
The content of the release agent is preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total mass of the toner particles.

-Other additives-
Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

- Characteristics of toner particles -
The toner particles may be toner particles having a single layer structure, or may be toner particles having a so-called core-shell structure composed of a core (core particle) and a coating layer (shell layer) that coats the core. The toner particles having a core-shell structure may be composed of, for example, a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing a binder resin.

The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less.
The volume average particle size of the toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter, Inc.) and an ISOTON-II (manufactured by Beckman Coulter, Inc.) electrolyte. For the measurement, 0.5 mg to 50 mg of a measurement sample is added to 2 ml of a 5% by mass aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte with the suspended sample is subjected to a dispersion treatment using an ultrasonic disperser for 1 minute, and the particle size of particles in the particle size range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000.

-External additives-
Examples of external additives include inorganic particles such as _SiO2 , TiO2, _Al2O3 , _CuO , ZnO, _SnO2 , _CeO2 , _Fe2O3 , MgO, BaO, _CaO , _K2O , _Na2O , _ZrO2 , CaO.SiO2, _K2O .( _{TiO2 ) n} , _Al2O3.2SiO2 , _CaCO3 , _MgCO3 , _BaSO4 , _{and MgSO4 .}

The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, but examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more.
The amount of the hydrophobic treatment agent is usually, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic particles.

Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).
The amount of the external additive added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

- Toner manufacturing method -
The toner is obtained by producing toner particles and then externally adding an external additive to the toner particles. The toner particles may be produced by either a dry production method (e.g., a kneading and pulverization method) or a wet production method (e.g., an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular restrictions on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

<Image forming apparatus, image forming method>
An image forming apparatus and an image forming method according to this embodiment will be described.
The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes the toner image transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning unit that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging unit that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging.
When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

In the image forming apparatus according to this embodiment, for example, the portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. A suitable process cartridge is, for example, a process cartridge equipped with developing means that contains the electrostatic image developer according to this embodiment.

The following describes an example of an image forming apparatus according to this embodiment, but the present invention is not limited to this. In the following explanation, the main parts shown in the figure will be described, and other parts will not be described.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment.
The image forming apparatus shown in Fig. 1 includes first to fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side horizontally spaced a predetermined distance apart from one another. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

An intermediate transfer belt (an example of an intermediate transfer body) 20 extends above each of the units 10Y, 10M, 10C, and 10K. The intermediate transfer belt 20 is wound around a drive roll 22 and a support roll 24 that contact the inner surface of the intermediate transfer belt 20, and runs in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 by a spring or the like (not shown) in a direction away from the drive roll 22, and tension is applied to the intermediate transfer belt 20 wound around them. An intermediate transfer belt cleaning device 30 is provided on the image bearing surface side of the intermediate transfer belt 20, facing the drive roll 22.
The developing devices (examples of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged, in order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it; a primary transfer roll (an example of a primary transfer means) 5Y that transfers the developed toner image onto the intermediate transfer belt 20; and a photoreceptor cleaning device (an example of an image carrier cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after primary transfer.

The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20, facing the photoreceptor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

The operation of forming a yellow image in the first unit 10Y will be described below.
First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y.
The photoreceptor 1Y is formed by laminating a photosensitive layer on a conductive substrate (for example, a volume resistivity of 1×10 ⁻⁶ Ωcm or less at 20°C). This photosensitive layer normally has high resistance (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the portion irradiated with the laser beam changes. Therefore, the charged surface of the photoreceptor 1Y is irradiated with a laser beam 3Y from the exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). As a result, an electrostatic charge image of a yellow image pattern is formed on the surface of the photoreceptor 1Y.

An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image.
The electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y travels. At this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

Developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner becomes frictionally charged as it is stirred inside developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on photoreceptor 1Y. As the surface of photoreceptor 1Y passes through developing device 4Y, yellow toner electrostatically adheres to the discharged latent image portion on the surface of photoreceptor 1Y, and the latent image is developed with yellow toner. Photoreceptor 1Y, with the yellow toner image formed, continues to travel at a predetermined speed, and the toner image developed on photoreceptor 1Y is transported to a predetermined primary transfer position.

When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in the first unit 10Y.
On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit.
In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are transferred onto the intermediate transfer belt 20 in a superimposed manner.

The intermediate transfer belt 20, onto which the four-color toner images have been multiply transferred through the first through fourth units, reaches a secondary transfer section consisting of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 positioned on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a supply mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The applied transfer bias has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image from the intermediate transfer belt 20 to the recording paper P. The secondary transfer bias is determined based on the resistance detected by a resistance detection means (not shown) that detects the resistance of the secondary transfer section, and is voltage-controlled.

The recording paper P with the transferred toner image is fed into the pressure contact area (nip area) between a pair of fixing rolls in the fixing device (an example of a fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image. Once the color image has been fixed, the recording paper P is conveyed toward the discharge section, completing the series of color image formation operations.

Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copying machines, printers, etc. In addition to the recording paper P, examples of the recording medium include overhead projector sheets and the like.
To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of ordinary paper is coated with a resin or the like, or art paper for printing, etc., is preferably used.

<Process cartridge>
The process cartridge according to this embodiment will be described.
The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.
The process cartridge according to this embodiment may be configured to include a developing means and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.
FIG. 2 is a schematic diagram showing an example of the process cartridge according to the present embodiment.
The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are combined and formed into a cartridge by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure.
In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium).

The following examples illustrate embodiments of the invention in detail, but the invention is in no way limited to these examples. In the following description, "parts" and "%" are by mass unless otherwise specified.

<Toner Production>
[Preparation of Resin Particle Dispersion (1)]
Ethylene glycol (FUJIFILM Wako Pure Chemical Corporation) 37 parts, neopentyl glycol (FUJIFILM Wako Pure Chemical Corporation) 65 parts, 1,9-nonanediol (FUJIFILM Wako Pure Chemical Corporation) 32 parts, terephthalic acid (FUJIFILM Wako Pure Chemical Corporation) 96 parts. The above materials were charged into a flask, and the temperature was raised to 200°C over 1 hour. After confirming that the reaction system was uniformly stirred, 1.2 parts of dibutyltin oxide was added. The temperature was raised to 240°C over 6 hours while distilling off the water produced, and stirring was continued at 240°C for 4 hours to obtain a polyester resin (acid value 9.4 mg KOH/g, weight average molecular weight 13,000, glass transition temperature 62°C). This polyester resin was transferred in a molten state to an emulsifier/disperser (Cavitron CD1010, Eurotech) at a rate of 100 g per minute. Separately, 0.37% diluted ammonia water, prepared by diluting reagent ammonia water with ion-exchanged water, was placed in a tank and heated to 120°C in a heat exchanger. The diluted ammonia water was then transferred to the emulsifying/dispersing machine at a rate of 0.1 L/min simultaneously with the polyester resin. The emulsifying/dispersing machine was operated under conditions of a rotor rotation speed of 60 Hz and a pressure of 5 kg/ ^cm2 , yielding a resin particle dispersion (1) with a volume average particle size of 160 nm and a solids content of 30%.

[Preparation of Resin Particle Dispersion (2)]
Decanedioic acid (Tokyo Chemical Industry Co., Ltd.) 81 parts Hexanediol (Fujifilm Wako Pure Chemical Industries, Ltd.) 47 parts The above materials were charged into a flask, the temperature was raised to 160 ° C. over 1 hour, and after confirming that the reaction system was uniformly stirred, 0.03 parts of dibutyltin oxide was added. The temperature was raised to 200 ° C. over 6 hours while distilling off the produced water, and stirring was continued at 200 ° C. for 4 hours. The reaction liquid was then cooled, solid-liquid separation was performed, and the solid was dried at 40 ° C. under reduced pressure to obtain polyester resin (C1) (melting point 64 ° C., weight average molecular weight 15,000).

The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra-Turrax T50, manufactured by IKA Corporation), and then dispersed using a pressure-discharge homogenizer. The dispersion was recovered when the volume average particle size reached 180 nm, yielding a resin particle dispersion (2) with a solids content of 20%.

[Preparation of Colorant Particle Dispersion (1)]
Cyan pigment (Pigment Blue 15:3, Dainichiseika Color & Chemicals Mfg. Co., Ltd.) 10 parts Anionic surfactant (Neogen SC, Dai-ichi Kogyo Seiyaku Co., Ltd.) 2 parts Ion-exchanged water 80 parts The above materials were mixed and dispersed for 1 hour using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain colorant particle dispersion (1) having a volume average particle size of 180 nm and a solids content of 20%.

[Preparation of Release Agent Particle Dispersion (1)]
Paraffin wax (HNP-9, Nippon Seiro Co., Ltd.) 50 parts Anionic surfactant (Neogen SC, Dai-ichi Kogyo Seiyaku Co., Ltd.) 2 parts Ion-exchanged water 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra-Turrax T50, IKA Corporation), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 200 nm, the particles were collected to obtain a release agent particle dispersion (1) with a solids content of 20%.

[Preparation of Toner (1)]
Resin particle dispersion (1) 150 parts, Resin particle dispersion (2) 50 parts, Colorant particle dispersion (1) 25 parts, Release agent particle dispersion (1) 35 parts, Polyaluminum chloride 0.4 parts, Ion-exchanged water 100 parts. The above materials were placed in a round stainless steel flask and thoroughly mixed and dispersed using a homogenizer (Ultra-Turrax T50, IKA Corporation). The flask was then heated to 48°C in an oil bath while stirring. The reaction system was maintained at 48°C for 60 minutes, and then 70 parts of Resin particle dispersion (1) were slowly added. The pH was then adjusted to 8.0 using a 0.5 mol/L aqueous sodium hydroxide solution. The flask was then sealed, the stirring shaft was magnetically sealed, and the mixture was heated to 90°C with continued stirring and maintained for 30 minutes. The mixture was then cooled at a rate of 5°C/min, solid-liquid separated, and thoroughly washed with ion-exchanged water. The solid-liquid separation was then carried out, and the resulting particles were redispersed in ion-exchanged water at 30° C. and washed by stirring for 15 minutes at a rotation speed of 300 rpm. This washing operation was repeated six more times, and when the pH of the filtrate reached 7.54 and the electrical conductivity reached 6.5 μS/cm, solid-liquid separation was carried out, and vacuum drying was continued for 24 hours to obtain toner particles (1) having a volume average particle size of 5.7 μm.

100 parts of the above toner particles (1) and 0.7 parts of hydrophobic silica (RY50 manufactured by Nippon Aerosil Co., Ltd.) were mixed in a Henschel mixer to obtain toner (1).

<Preparation of carrier>
[Preparing the core material]
-Ferrite particles-
74 parts _{of Fe2O3} , 4 parts of Mg(OH) ₂ , and 21 parts of _MnO2 were mixed and pre-fired in a rotary kiln at 950°C for 7 hours (first time). The resulting pre-fired product was pulverized in a wet ball mill for 7 hours to an average particle size of 2.0 μm, and then granulated using a spray dryer. The resulting granulated product was pre-fired in a rotary kiln at 950°C for 6 hours (second time). The resulting pre-fired product was pulverized in a wet ball mill for 3 hours to an average particle size of 5.6 μm, and then granulated using a spray dryer. The resulting granulated product was fired in an electric furnace at 1300°C for 5 hours. The resulting fired product was crushed and classified to obtain ferrite particles with a volume average particle size of 32 μm.

[Preparation of nitrogen-containing silica particles]
-Nitrogen-containing silica particles (1)-
Eight parts of silica (volume average particle size 12 nm) was added to 100 parts of toluene and dispersed by stirring using an ultrasonic disperser, and then 2 parts of 3-aminopropyltriethoxysilane was added and the mixture was stirred at room temperature for 1 hour. After that, the toluene was distilled off and the mixture was dried, and the mixture was heated at 120°C for 30 minutes to complete the reaction of the aminosilane polymer, thereby obtaining aminosilane-treated nitrogen-containing silica particles (1) (silica:aminosilane mass ratio = 8:2).
-Nitrogen-containing silica particles (2) to (7)-
Nitrogen-containing silica particles (2) to (7) were obtained in the same manner as in the production of nitrogen-containing silica particles (1), except that silica having a volume average particle size of 3 nm, 5 nm, 8 nm, 15 nm, 20 nm, or 33 nm was used instead of silica having a volume average particle size of 12 nm.

[Preparation of nitrogen-containing resin fine particles]
The nitrogen-containing resin fine particles used were crosslinked melamine resin fine particles having volume average particle diameters of 100 nm, 150 nm, 200 nm, 250 nm and 300 nm.

[Example 1]
Ferrite particles 100 parts Nitrogen-containing silica particles (1) 1.55 parts (30% by mass based on the total mass of the resin coating layer)
Nitrogen-containing resin fine particles (volume average particle size 200 nm) 0.55 parts (10% by mass based on the total mass of the resin coating layer)
(mass ratio of nitrogen-containing resin particles to nitrogen-containing silica particles: 0.33)
- 3 parts cyclohexyl methacrylate/methyl methacrylate copolymer (copolymerization ratio 95 mol:5 mol) - 14 parts toluene Of the above materials, nitrogen-containing silica particles (1), nitrogen-containing resin microparticles, cyclohexyl methacrylate/methyl methacrylate copolymer, toluene, and glass beads (diameter 1 mm, same amount as toluene) were placed in a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1200 rpm for 30 minutes to obtain a resin layer forming solution (1).
The ferrite particles were placed in a vacuum degassing kneader, and the resin layer forming solution (1) was then added. The mixture was heated and depressurized with stirring to evaporate the toluene, and the ferrite particles were coated with the resin. Then, fine and coarse powders were removed using an elbow jet to obtain a carrier.

[Examples 2 to 20]
Carriers of each example were prepared in the same manner as in Example 1, except that the types and contents of the nitrogen-containing silica particles and nitrogen-containing resin fine particles were set to the specifications shown in Table 1.
[Comparative Example 1 and Comparative Example 2]
A carrier was prepared in the same manner as in Example 1, except that the types and contents of the nitrogen-containing silica particles and nitrogen-containing resin fine particles were set to the specifications shown in Table 1.
<Carrier particle properties>
The following values were determined for the carriers obtained in Examples 1 to 20 and Comparative Examples 1 and 2, and are shown in Table 1.
Resin coating layer thickness T (μm)
Measurements were carried out according to the methods described.
D/T (volume average particle diameter of nitrogen-containing resin fine particles/thickness of resin coating layer)
The volume average particle diameter of each nitrogen-containing resin fine particle, such as 100 nm, was converted into μm units to determine D (μm), and D/T was calculated using the thickness T (μm) of the resin coating layer.

In Table 1, the content of the nitrogen-containing silica particles represents the content relative to the total mass of the resin coating layer.
In Table 1, the content of the nitrogen-containing resin particles represents the content relative to the total mass of the resin coating layer.

<Adjustment of Developer>
Twenty types of developers were prepared by mixing 100 parts of each of the carriers of Examples 1 to 20, Comparative Examples 1 and 2 with 8.5 parts of the toner (1). The prepared developers were used in the following evaluation of charge retention.

<Evaluation of Charge Retention of Developer>
The developer was placed in the developing device in the black position of an image forming apparatus ("Iridesse Production Press" manufactured by Fujifilm Business Innovation Co., Ltd.). A total of 50,000 sheets were printed using this image forming apparatus under conditions of a low temperature and low humidity environment (10°C, 15% RH) with 100 sheets of A4 paper printed per job. Approximately 20 g of the developer was sampled initially and after 50,000 sheets were printed. The toner was removed from the developer by blow-off, and only the carrier was isolated. 0.8 g of the toner used in preparing the developer was added to the resulting carrier per 10 g of carrier, and the mixture was stirred for 5 minutes in a turbulent mixer, and the charge amount was measured.
The carrier charge ratio (charge ratio after printing 50,000 sheets to the initial charge ratio) was calculated for the initial developer and the developer after printing 50,000 sheets, and the toner charge retention was evaluated according to the following criteria. The results are shown in Table 1.
A: The carrier charge ratio is 0.9 or more. B: The carrier charge ratio is 0.8 or more and less than 0.9. C: The carrier charge ratio is 0.7 or more and less than 0.8. D: The carrier charge ratio is less than 0.7.

As shown in Table 1, the electrostatic image developing carriers of the examples were found to suppress deterioration in charge retention compared to the electrostatic image developing carriers of the comparative examples.

1Y, 1M, 1C, 1K: photoconductor (an example of an image carrier)
2Y, 2M, 2C, 2K: charging roll (an example of a charging means)
3. Exposure device (an example of an electrostatic image forming means)
3Y, 3M, 3C, 3K: Laser beams 4Y, 4M, 4C, 4K: Developing device (an example of developing means)
5Y, 5M, 5C, 5K: Primary transfer roll (an example of a primary transfer means)
6Y, 6M, 6C, 6K: Photoconductor cleaning device (an example of an image carrier cleaning means)
8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K image forming unit 20 intermediate transfer belt (an example of an intermediate transfer body)
22 Drive roll 24 Support roll 26 Secondary transfer roll (an example of a secondary transfer means)
28 Fixing device (an example of fixing means)
30 Intermediate transfer belt cleaning device (an example of an intermediate transfer body cleaning means)
P Recording paper (an example of a recording medium)

107 Photoreceptor (an example of an image carrier)
108 Charging roll (an example of charging means)
109 Exposure device (an example of an electrostatic image forming means)
111 Developing device (an example of developing means)
112 Transfer device (an example of transfer means)
113 Photosensitive member cleaning device (an example of an image carrier cleaning means)
115 Fixing device (an example of fixing means)
116 Mounting rail 117 Housing 118 Opening for exposure 200 Process cartridge 300 Recording paper (an example of a recording medium)

Claims (15)

A core material and
a resin coating layer containing nitrogen-containing silica particles and nitrogen-containing resin fine particles and coating the core material;
and
the content of the nitrogen-containing silica particles is 10% by mass or more and 55% by mass or less with respect to the total mass of the resin coating layer,
the nitrogen-containing resin fine particles have a volume average particle size of 100 nm or more and 250 nm or less;
The carrier for developing electrostatic images has a mass ratio P/S of the mass S of the nitrogen-containing silica particles to the mass P of the nitrogen-containing resin fine particles of 0.15 or more and 0.55 or less. The carrier for developing electrostatic images according to claim 1, wherein the nitrogen-containing silica particles include silica particles treated with a silane coupling agent having a nitrogen-containing functional group, or a vinyl copolymer synthesized from a (meth)acrylic monomer having a nitrogen-containing functional group and a hydrolyzable alkoxysilanol group. The carrier for developing electrostatic images according to claim 2, wherein the silane coupling agent having a nitrogen-containing functional group has an amino group and a hydrolyzable alkoxysilanol group. The carrier for developing electrostatic images according to claim 3, wherein the volume average particle size of the nitrogen-containing silica particles is 5 nm or more and 20 nm or less. The carrier for developing electrostatic images according to claim 1, wherein D/T is 0.007 or more and 0.24 or less, where D (μm) is the volume average particle diameter of the nitrogen-containing resin microparticles and T (μm) is the thickness of the resin coating layer. The carrier for developing electrostatic images according to claim 5, wherein the content of the nitrogen-containing resin particles is 5% by mass or more and 30% by mass or less relative to the total mass of the resin coating layer. The carrier for developing electrostatic images according to claim 5, wherein the volume average particle diameter of the nitrogen-containing resin microparticles is 120 nm or more and 230 nm or less. The carrier for developing electrostatic images according to claim 1, wherein the resin coating layer contains an alicyclic (meth)acrylic resin. The carrier for developing electrostatic images according to claim 8, wherein the alicyclic (meth)acrylic resin contains cyclohexyl (meth)acrylate as a polymerization component. The carrier for developing electrostatic images according to claim 1, wherein the content of the nitrogen-containing silica particles is 13% by mass or more and 50% by mass or less relative to the total mass of the resin coating layer. The carrier for developing electrostatic images according to claim 10, wherein the mass ratio P/S of the nitrogen-containing resin fine particles to the mass S of the nitrogen-containing silica particles is 0.18 or more and 0.52 or less. a toner for developing an electrostatic image;
The electrostatic image developing carrier according to any one of claims 1 to 11,
1. An electrostatic image developer comprising: a developing unit containing the electrostatic image developer according to claim 12 and developing an electrostatic image formed on the surface of an image carrier into a toner image by using the electrostatic image developer,
A process cartridge is detachably mounted in an image forming apparatus. an image carrier;
a charging means for charging the surface of the image carrier;
an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier;
a developing unit containing the electrostatic image developer according to claim 12 and developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer;
a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium;
a fixing means for fixing the toner image transferred onto the surface of the recording medium;
An image forming apparatus comprising: a charging step of charging the surface of the image carrier;
an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier;
a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to claim 12;
a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium;
a fixing step of fixing the toner image transferred onto the surface of the recording medium;
An image forming method comprising the steps of: